Muscle lactate dehydrogenase activity is decreased in murine motor neuron disease.

Lactic dehydrogenase (LDH) activity was examined in affected skeletal muscles of the wobbler mouse, a murine model in which denervation follows degeneration of spinal cord motoneurons. Average biceps brachii LDH activity was reduced at 7 and 15 but not at 3 postnatal weeks. These results demonstrate a progressive alteration in muscle energy metabolism in a natural model of motor neuron disease.

The muscle-tendon junctions of fast and slow fibres in the garter snake: ultrastructural and stereological analysis and comparison with other species.

The muscle-tendon junctions of fast and slow muscle fibres from the costocutaneous muscles of garter snakes have been analyzed by scanning and transmission electron microscopy and by a stereological protocol. The junctions of the two fibre types are morphologically similar, and consist of anastomosing processes which increase the surface area of the muscle-tendon interface and significantly reduce the stress at the junction when the fibres contract. The muscle-tendon junctions of these fibres are analogous to adhesive joints between stiff adherends and fibre-reinforced composite materials. Stereological estimates of the area of surface membrane devoted to force transmission, relative to the cross-sectional area of myofilaments (the 'interfacial ratio'), have produced values of about 14 for the fast fibres and about 16 for the slow fibres. This difference is small but statistically significant. Interfacial ratios of about 14 and 10 were previously determined for fast and slow fibres, respectively, of both chickens and mice. Thus the slower fibres of the snake differ from those of the mouse and chicken, in that their interfacial ratio is greater than that of fast fibres.

A stereological comparison of the muscle-tendon junctions of fast and slow fibers in the chicken.

Transmission of contractile tension from skeletal muscle fibers to connective tissue elements is thought to occur at the muscle-tendon junctions, specialized regions at the extreme ends of the fibers. Previous work has suggested that the structure of this region may be quantitatively modified to match the contractile properties of the fibers. Using scanning electron microscopy, transmission electron microscopy, and stereological analysis, we have analyzed the three-dimensional structure, and have quantitatively compared the muscle-tendon junctions, of slow and fast fibers of the anterior (ALD) and posterior (PLD) latissimus dorsi muscles of the chicken. The ends of ALD and PLD fibers are found to be structurally different in some respects but to be similar with respect to their surface specializations, which are believed to function in the transmission of tension. Quantitative analysis of these specializations indicates that, when referred to similar cross-sectional areas of myofilaments, the fast fibers of the PLD have approximately 40% more surface area devoted to force transmission than do the slow fibers of the ALD. These observations are consistent with the idea that the amount of cell surface specialized for force transmission is related to the functional properties of the muscle fiber.